Theory question: IAC/PCV
A PCV valve stuck open seems like it would look exactly like a stuck open IAC at idle, since blow-by gasses are very low at idle.
In a MAF engine, a stuck open IAC would allow too much air into the intake, but that air is metered by the MAF since the IAC is downstream of the MAF. A stuck open PCV valve would also allow too much air into the intake, but again that air is metered, since the fresh air inlet is downstream of the MAF. So it seems that injection pulse would be matched by the PCM for the volume of air metered by the MAF in both a stuck open PCV and stuck open IAC.
In a MAP engine, a stuck open PCV valve would be constantly dumping air into the intake but would be seen (metered) by the MAP sensor as an increased load. A stuck open IAC would again be dumping unwanted air into the intake manifold but that air would be seen (metered) by the MAP sensor as an increased load.
I understand that at idle, you wouldn't want all that extra fuel and air, so the engine would run rough, and maybe stall. The combustion process would probably send a bunch of unburned O2 and raw fuel down the tailpipe. And an O2 only registers the presence and absence of oxygen, so it would give a lean code with the unburned O2.
Is this accurate? Or am I missing something?
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A PCV valve stuck open seems like it would look exactly like a stuck open IAC at idle, since blow-by gasses are very low at idle.
In a MAF engine, a stuck open IAC would allow too much air into the intake, but that air is metered by the MAF since the IAC is downstream of the MAF. A stuck open PCV valve would also allow too much air into the intake, but again that air is metered, since the fresh air inlet is downstream of the MAF. So it seems that injection pulse would be matched by the PCM for the volume of air metered by the MAF in both a stuck open PCV and stuck open IAC.
Generally agree. The only variable would be if the PCV system is strong enough to suck air past the crankshaft seals. On some older domestic PCV systems, the metering orifice just doesn't produce that much suction, even at full flow. But many Euro makes/models, the PCV has the ability to suck air past seals, creating a vacuum leak and unmetered air.
In a MAP engine, a stuck open PCV valve would be constantly dumping air into the intake but would be seen (metered) by the MAP sensor as an increased load. A stuck open IAC would again be dumping unwanted air into the intake manifold but that air would be seen (metered) by the MAP sensor as an increased load.
This sounds right? But again, never ran into it firsthand. I don't have any MAP vehicles to experiment on, either.
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